1. Field of the Invention
The present invention relates to an endoscopic hood having a cylindrical hood main body attached to an end portion of an insertion portion of an endoscope.
2. Description of the Related Art
Generally, an endoscopic hood may be used in a state that it is attached to an end portion of an insertion portion of an endoscope in some cases. This endoscopic hood is attached in a state that it is detachably disposed to an end portion of an insertion portion or that it is integrally fixed to the same.
FIG. 7A shows a state that a conventional endoscopic hood b is attached to an end portion of an insertion portion a of an endoscope. Here, to an end surface a1 of the insertion portion a of the endoscope are provided an object lens c of an observation optical system and an illumination lens d of an illumination optical system, respectively. Further, an observation visual field is illuminated with illumination light rays emitted from the illumination lens d. At this moment, an observation image in the observation visual field in an illumination range illuminated with the illumination light enters the object lens c. As a result, the observation image of the endoscope is displayed on a screen of, e.g., a monitor.
Furthermore, a substantially cylindrical hood main body ba is provided to the endoscopic hood b. A fixed portion b2 fixed to the end portion of the insertion portion a of the endoscope is provided on a base end side of this hood main body b1.
Moreover, a protruding portion b3 which protrudes in an observation visual field direction of the endoscope is extended to the end portion of this fixed portion b2. Additionally, when an end surface a1 of the insertion portion a of the endoscope approximates an intraluminal wall surface, the protruding portion b3 is designed to come into contact with the intraluminal wall surface before the object lens c of the observation optical system is brought into contact with the intraluminal wall surface. As a result, the endoscopic hood b prevents the object lens c of the observation optical system exposed on the end surface a1 of the insertion portion a from directly coming into contact with the intraluminal wall surface.
In observation using the endoscope, incident light rays entering the object lens c are restricted within a range of an extension line (indicated by a solid line in FIG. 7A) running between an end edge of the protruding portion b3 of the endoscopic hood b and the object lens c. Further, the distance between a living tissue as an observation target and the object lens c and a display range (observation range) of the living tissue as an observation target inserted into the observation visual field of the object lens c varies in proportion. Therefore, when the distance between the living tissue as the observation target and the object lens c is large, the range of the observation target inserted into the observation visual field of the object lens c becomes large. For example, when performing an operation to search for a target diseased part, this operation is carried out in a state that the distance between the living tissue as the observation target and the object lens c is large and the display range of the living tissue is wide.
Furthermore, after the target diseased part is found, the end portion of the insertion portion a of the endoscope is caused to approximate the target diseased part. As a result, the target diseased part is magnified as much as possible and displayed in detail. At this moment, by bringing the end of the protruding portion b3 of the endoscopic hood b into contact with the living tissue, the distance between the living tissue as the observation target and the object lens c is maintained as a fixed distance.
Moreover, Jpn. Pat. Appln. KOKAI publication No. 2001-224550 discloses a structure that an inner wall part of the endoscopic hood is formed into a square-built shape along an outer edge of the observation visual field of the rectangular observation optical system. This prevents the rectangular observation visual field of the observation optical system from being cut off by the inner wall part of the endoscopic hood.
Meanwhile, the endoscopic hood b may be used in a state that the end portion of the protruding portion b3 is in contact with the living tissue in some cases. Therefore, the endoscopic hood b3 is generally formed of a soft material such as rubber. This soft material such as rubber cannot transmit the light therethrough. Thus, in observation using the endoscope, the irradiation range of the illumination light emitted from the illumination lens d is restricted by an end position of the protruding portion b3 of the endoscopic hood b.
Additionally, even when the endoscopic hood b is used with the end portion of the protruding portion b3 being in contact with the living tissue, the object lens c of the observation optical system must be focused on the living tissue. Therefore, a fixed length is required as a protrusion length of the protruding portion b3 of the endoscopic hood b.
Further, the object lens c and the illumination lens d on the end surface a1 of the insertion portion a of the endoscope are arranged at positions displaced in a direction orthogonal to an axial direction of the insertion portion a of the endoscope. Therefore, as shown in FIG. 7A, a deviation occurs in an irradiation range (irradiation angle α) of the illumination light emitted from the illumination lens d indicated by the chain double-dashed line in FIG. 7A and a visual field range (observation angle β) of an observation image entering the object lens c indicated by a solid line in FIG. 7A.
Here, when the endoscopic hood b that the protrusion length of the protruding portion b3 of the endoscopic hood b is set at a limit position which is not included in the visual field range of the object lens c is attached at the end portion of the insertion portion a of the endoscope, the protruding portion b3 of the endoscopic hood b is not inserted into the visual field range of the object lens c. In this case, however, a part of the illumination light with which the visual field range of the object lens c is irradiated is cut off by the protruding portion b3 of the endoscopic hood b. Therefore, as shown in FIG. 7B, there is a problem of occurrence of so-called vignetting of the illumination light that a shadow f of the protruding portion b3 of the endoscopic hood b is inserted into an observation image of the endoscope displayed in a screen e of a monitor. In this case, there is generated a problem that the display range of the observation image of the endoscope displayed in the screen e of the monitor is narrower than the visual field range of the observation image entering the object lens c.
In view of the above-described problems, it is an object of the present invention to provide an endoscopic hood with an excellent observation performance, which can reduce shadow in an observation screen of an endoscope caused due to vignetting of the illumination light without degrading the function of the hood main body.